It is common practice to adjustably tilt the axis of rotation of an idler pulley or drum over which a sanding belt is trained so as to compensate for slight variations in the length of the edges of the belt and slight alignment errors in the machine which would otherwise cause the belt to run off center. However, in an arrangement wherein a swinging idler drum has two spaced positions in which it engages opposite sides of a sanding belt to tension it, thereby to facilitate diverse sanding operations, opposite tilting of the drum axis when in these positions is usually required to maintain belt tracking. It is also desirable that tracking mechanism for such an arrangement provides for independently adjusting the tilt of the idler drum axis for each of its two positions and further provides that such independent adjustments once made are automatically re-established when the idler drum is returned to either position.